In the field of heavy duty mining or construction, a number of different types of trailers (often referred to as lowboys) are utilized to move equipment such as shovels, earth moving apparatus and the like. Some trailers are rear loading meaning that the equipment to be hauled is loaded onto the trailer bed from the trailer rear, whereby the front end is used for hitching the trailer to a hauling vehicle.
Other trailers are front loading, wherein a front end portion of the trailer serves a dual capacity as a hitching point for trailer movement, and a loading/unloading point for equipment to be hauled.
FIG. 1 shows a typical lowboy trailer 90 having a trailer bed 91 for supporting heavy machinery 92, a gooseneck hitching assembly 93, a hauling vehicle 95, trailer wheels 97 (one shown), and a trailer axle assembly represented by numeral 99. The gooseneck hitching assembly 93 is disclosed in Smith's U.S. Pat. No. 5,435,586, which is herein incorporated by reference in its entirety. Other heavier duty trailers of this type can be used with a drive for the rear wheels.
As shown in FIGS. 1-2B, the trailer 90 has a front end assembly 101 that links to center support rails 103 and outside rails 103′ at an interface 102, the rails 103, 103′ extending longitudinally along at least the trailer bed length. Generally, the center rails 103 extend beyond the trailer bed to provide support for the axle assembly 99. Although not shown, wooden or other material decking extends along the support rails 103, 103′ to provide a travel and support surface for the equipment during loading, unloading, and transport.
The assembly 101 is formed with a box beam construction. That is, a number of plates and support members are arranged and connected together to form an integral box-like structure that can transmit forces applied during raising of the trailer to the trailer support rails 103, 103′ and cross members as described below. The assembly 101 includes a top plate 104, which further comprises two ramp sections 105, and a center section 107. Also provided are side walls 109 and a bottom plate 111. A pickup shaft 113 is positioned in an opening 114, the shaft 113 held in place by four vertical plates 115 that extend between the interface 102 and the bottom plate 111. The center plate 107 also has a raised contact surface 117 to receive the tow member 127 of the hitch assembly 93, but the entire plate could act as a contact surface if so desired. A number of other longitudinal members make up the box beam, including insert plates 116 that extend beyond the interface 102, and angled insert plates 118. Each of the insert plates provides further strengthening against the load traveling across the ramp plates 105. U-shaped plates 120 extend beyond the interface 102 and a portion thereof buts against a web of each rail 103, 103′, the plates 120 facilitating attachment between the assembly 101 and the rails 103, 103′. In general, the various plates and members are either welded or bolted together to form the overall assembly 101.
As shown in FIG. 2B, the trailer bed with rails 103, 103′ (preferably I-shaped in cross section) employs cross members 106 (also preferably I-shaped) that are arranged at spaced apart intervals along the trailer bed length.
Prior to an exemplary loading procedure and with reference to FIG. 1 again, the front end assembly 101 of the trailer is laid on a ground surface, and the hitch assembly 93 is removed. Equipment is then driven onto the trailer bed, and the trailer front end is lifted in the following manner. With the tow member 122 in a raised position by retraction of a piston (not shown) connected at 124, the hitch 123 of the assembly 93 is positioned beneath the pickup shaft 113. The grab hook 125 pivots downwardly to engage the shaft 113 so that it is securely held by the hook 125 and hitch 123. Then, the tow member 122 is lowered to contact the center plate 107 and contact area 117. Once in contact with the center plate and contact surface, further extension of the piston raises the trailer as shown in FIG. 1. During this lifting operation, the lifting force is tremendous, and a heavy duty box beam construction, including the ramp portions, is required to evenly distribute the load initially applied to the front end assembly of the trailer to the ends of the four longitudinal support rails 103, 103′. Because of immense trailer loads, i.e., the support rails are typically dimensioned with 30 inch heights, and the box beam dimension at the interface 102 approximates this height. The front end assembly then tapers from this height to its free end.
One problem with these types of lowboy trailers is their inability to easily accommodate equipment that may be smaller in size than the machinery that the trailer typically supports. Many of the small mining or construction machines or equipment have components with low ground clearances due to their size. As a result and referring to FIG. 3, when loading a drilling machine 200, for example, the machine component 201 may only have a ground clearance of 18 inches. Further, the component 201 is relatively close to the tracks 203 of the machine 200. Consequently, if the machine were to be loaded the way large equipment is loaded, the component 201 would strike the center plate 107 before the tracks 203 of the machine reaches the trailer ramps 208. Consequently, alternative means must be employed to load these smaller machines onto the trailer bed. Loading blocks placed either at the trailer front end or at spaced apart intervals from the trailer front end have been used. However, in certain instances, the loading blocks must be made higher than the front end initial height, thereby causing the equipment to travel over a hump, and creating a state of instability. Other remedies include side loading of the trailer, although this creates safety issues, and runs counter to the purpose of the trailer's intended front end loading.
Therefore, a need has developed to provide a trailer, which can not only load 200-400 ton and heavier equipment, but is also versatile enough to load smaller equipment without requiring modification of the loading procedure.
Merely changing the slope of the trailer by reducing the height of the support beams is not a solution to the problem due to the loads that the trailer encounters during its lifting operation. Such a change would compromise the load bearing ability of the front end assembly.
The invention solves the problem faced by the prior art by providing a trailer front end assembly that is dimensioned to receive small equipment having components with a low ground clearance, while still maintaining the capability of supporting large equipment during a loading operation. The invention eliminates the need for another trailer, or time-consuming and/or unsafe loading procedures with a large trailer. The invention also provides a reduction in manufacturing costs and trailer assembly time/costs by simplifying the design of the front end assembly, and reduces the number of load bearing components.